1. Field of the Invention
The present invention relates to an optical disc device compatible with multilayer optical discs having a plurality of recording layers on one side, as well as to a focus jump method for multilayer optical discs having a plurality of recording layers on one side.
2. Description of the Related Art
In recent years, multilayer optical discs having a plurality of recording layers on one side have been prevailing. For an optical disc device compatible with multilayer optical discs, at is necessary that the focus position of laser light emitted from the optical pickup be changed over among a plurality of recording layers during recording operation of information onto a multilayer disc or reproducing operation of information recorded on a multilayer disc. For this purpose, the optical disc device compatible with multilayer optical discs makes a focus jump for moving the focus position from a current recording layer to a target recording layer.
As to the focus jump, first, a pulse signal called kick pulse is fed as a focus drive signal to an actuator that drives an objective lens included in the optical pickup. As a result, the objective lens is accelerated and moved in a focus direction. Thereafter, when a focus error signal has satisfied a brake start condition, a pulse signal called brake pulse and directed inverse to the kick pulse is fed as a focus drive signal to the actuator. Thus, the objective lens is decelerated and stopped, so that the focus jump is completed.
Given large crosstalk of the focus error signal before the focus jump, the jump start position is varied, resulting in an unstable focus jump. Also, given that a large fake signal has occurred in the focus error signal during a focus jump, it may occur that the fake signal triggers the brake start condition so as to start braking at an erroneous position or to cause the brake start timing to be delayed by an effect of the fake signal, thus the focus jump becoming unstable.
In JP 2008-130121 A, a focus drive signal generated from a focus error signal of the astigmatic method is used for a focus jump with an aim of stabilizing the focus jump. Due to this, JP 2008-130121 A describes no proposal as to the stabilization of the focus jump using the focus drive signal generated from a focus error signal of the differential astigmatic method.
With use of a focus drive signal generated from a focus error signal of the differential astigmatic method, it is known that a fake signal is generated in the focus error signal due to stray light of the sub beam or the like during a focus jump. Against the occurrence of this fake signal, JP 2002-367193 A and JP 2010-218609 A take a countermeasure that no decision as to the focus position is done upon occurrence of a fake signal. However, with this countermeasure taken, there arises a need for grasping occurrence of the fake signal, causing complicated control to be involved as another problem.